Photoflash lamp



June 29, 1965 p, D. JOHNSON 3,191,406

PHOTOFLASH LAMP Filed Dec. 26, 1961 lnventor:

PWD /oh son,

s Attorney;

United States Patent 3,191,406 PHGTOFLASH LAMP Peter D. Johnson,Schenectady, N.Y., assignor to General Electric Company, a corporationof New York Filed Dec. 26, 1961, Ser. No. 161,803 3 Claims. (Cl. 67-31)The present invention relates to photoilash lamps in general. Moreparticularly, the invention relates to photoflash lamps having increasedburning temperature and consequent higher eficiency of chemical energyinto light, higher color temperature and higher brightness.

Photofiash lamps presently utilized in photographic and allied artsgenerally are either of the primer type as disclosed and claimed in US.Patent 2,291,98 Pipkin or of the wire or foil type as disclosed andclaimed in U.S. Patent 1,776,637-Ostermeier. In the former typephotoflash lamp actinic light is produced solely by the burning of asolid combustible mixture coated upon the lamp electrode or filament,while in the latter type actinic light is produced primarily by theburning of a combustible material which may be metallic wire, shreddedfoil or crumpled foil distributed throughout the lamp envelope. Otherforms of lamps. may be utilized which include a combination or somemodification of these two basic type lamps. Actinic light is generallydefined as light capable of inducing chemical changes, as for instancein the emulsion of a photographic plate.

It is a principal object of the present invention to provide photoflashlamps of the aforementioned types having a high efliciency of conversionof chemical energy into actinic light.

Still another object of the invention is to provide photoilash lampshaving higher color temperatures and higher peak intensities.

Briefly stated, in accord with the present invention I provide improvedphotoflash lamps having increased energy conversion, higher colortemperatures and higher brightness in which the combustible materialconsist essentially of thorium, preferably of high purity.

The novel features believed characteristic of the in vention are setforth in the appended claims. The invention itself, however, togetherwith further objects and advantages thereof may best be understood byreference to the following description, taken in connection with theaccompanying drawing in which the sole figure is a verticalcross-sectional view, of a photoflash lamp illustrating the invention.

In the drawing, a photoflash lamp constructed in accord with theinvention comprises a hermetically sealed envelope or bulb 1 of asuitable light transmitting material such as glass, having a neckportion 2 and a solid re-entrant portion 3. A suitable base 4 is securedto neck portion 2 as by cementing or other suitable means. Bulb 1 isfilled with a combustion-supporting gaseous filling which may be oxygenor a suitable oxygenous or oxidizing gas, a pressure of approximately0.2 to 2 atmospheres, but preferably approximately 1 atmosphere. Bulb 1may be coated on its inner or outer surface, preferably on bothsurfaces, with a coating of a suitable light transmitting lacquer orvarnish to minimize shattering and cracking of the bulb on flashing andto render the bulb substantially shatter proof.

Sealed to the re-entrant portion 3 of bulk 1 and extending thereintofrom the neck portion 2 thereof are a pair of leadin Wires 5. Bridgingthe interior ends of wires 5 is a small ignition filament 6 which maycomprise a length of wire of a suitable high resistance material such astungsten. Mounted near the inner ends of leadin wires 5 and at leastpartially embedding filament 6 are thin coatings '7 of a suitable primeror combustible material causing an initial ignition flash within3,191,406 Patented June 29, 1965 the lamp envelope upon an applicationof an electric potential to wires 5. The primer material comprisingcoatings 7 may conveniently comprise a powdered mixture of a readilycombustible metal such as zirconium and an oxygen liberating substancesuch as potassium chlorate or potassium perchlorate bonded together by asuitable binder such as nitrocellulose. The interior of bulb 1 is fi ledwith a flocculent metallic mass '8 of combustible actinic lightproducing material, which in accord with the invention, comprisesthorium. This light producing material may be in the form of fine wireshredded foil or crumpled leaf foil. Combustible material 8 is composedof thorium metal having at least purity which has been protected fromoxidation so as to be readily reactive with oxygen at the combustiontemperature.

Conventional photoflash bulbs used heretofore are similar to the bulbsof my invention, but utilized, as the fiocculent metallic mass ofactinic light producing material, generally aluminum or magnesium.Numerous other materials have been mentioned for this type materialincluding copper, iron, nickel, and rare earths generally. The staplematerials utilized, however, generally constitute aluminum and/ormagnesium.

In accord with my invention, the thorium metal is of 95% purity orbetter and is unoxidized. If it is in the form of a leaf foil it shouldbe of a thickness of 0.001" or less, and is preferably shredded intofine shreds to be more readily combustible in a short period of time. Incertain instances When long combustion period is desired foil orshredded foil of thickness greater than 0.001 may be used, thusfacilitating a longer burning time. in bulbs of the invention light isactually emitted by excited thorium oxide produced by the reaction ofthorium with the atmosphere in the bulb.

The atmosphere within bulb 1 generally comprises oxygen. When mixturesof oxygen and nitrogen are used nitrogen may react with thorium andcontribute to the light output. The amount of oxygen and of thorium inthe bulb depends upon the size and volume of the bulb. In oneembodiment, a 7 cubic centimeter approximate volume bulb utilizesapproximately 60 milligrams of shredded foil thorium and an oxygenpressure of 1000 millimeters of mercury. In another embodiment a 25cubic centimeter approximate volume bulb was utilized and containedmilligrams of thorium and utilized oxygen at a pressure of 700millimeters of mercury.

In general, the ratio of thorium to oxygen within the bulb varies withinthe range of from 5 to 25 milligrams of thorium per cubic centimeter ofoxygen at atmospheric pressure.

The criteria of measurement of a material as an actinic light source ina photoflash lamp are the color temperature, the peak intensity and theefiiciency of conversion of chemical energy into light energy. Colortemperature generally refers to the absolute temperature in degrees.Kelvin of a theoretical black body radiator whose color appearancematches that of the light source being measured. For conventionalphotoflash lamps utilizing aluminum as the actinic light source andwhich are generally utilized commercially today, the average colortemperature is approximately 3800 K. Lamps constructed in accord withthis invention, although not in mass production to the extent that anaverage color temperature can be reached with exact precision, generallyshow an average color temperature of the order of 4500 K., with somemeasurements going as high as 5000 K. Accordingly, in the measurement ofcolor temperature photoiiash lamps constructed of high purity unoxidizedthorium are highly advantageous and superior to present day commercialphotoflash lamps.

Another criteria of photoilash lamps is the peak intensity of the lightemitted by the lamp. This is dependent on the temperature of theradiating material and, according to Plancks Radiation Law, increasesrapidly with increase in temperature. Calculations made from the thoriumlamps which have been constructed in accord with the present inventionindicate a maximum peak intensity of these lamps which is approximately4 to 6 times greater than the average peak intensity of aluminum filledphotoflash lamps. Finally, the efficiency of conversion of chemicalenergy into light energy is approximately for lamp constructed in accordwith the present invention as compared with 10% for conventionalaluminum One specific example, given for illustrative purposes only andnot to be construed in a limiting sense, of a preferred embodiment ofthe invention comprises the lamp as illustrated in the drawing andhaving an elliptical glass envelope with a major axis of 1.58" and aminor axis of 1.38". The bulb has a volume of approximately cubiccentimeters and is filled with 0.001" thick unoxidized thorium metalhaving a purity of approximately 98% shredded into filaments ofapproximately 0.001" width and amounting to a total Weight ofapproximately 175 milligrams of thorium metal. The remainder of the bulbis filled with oxygen gas at a pressure of approximately 1 atmosphere.The primer coating on the load wires is approximately long andapproximately 0.003" thick. The filament is a 0.0007 diameter tungstenwire.

In accord with another embodiment of the present invention, the thoriumactinic light producing material may be included in the primer beads 7which are, consequently made much greater in weight, and the shreddedfoil 8 is thereby eliminated from the envelope. As with the embodimentillustrated in the drawing wherein beads '7 merely comprise a starterthe combustible material, thorium replaces the zirconium and is in theform of a finely divided powder having a purity of 95% or better andunoxidized. One specific example of a bulb constructed with in accordwith this embodiment was a bulb, as in the first example, having avolume of approximately 25 cubic centimeters in which the totalcombustible mixture of both beads 7 comprise approximately milligramthorium powder and milligram potassium perchlorate. The bulb was alsofilled with oxygen to a pressure of approximately 300 millimeters ofmercury. Alternatively, ammonium perchlorate could be utilized insteadof the potassium perchlorate.

The photoflash lamps of this invention may be produced in accord withthe standard manufacturing techniques. The lamp illustrated in thedrawing utilizing a Wire of foil type actinic light producingcombustible material may be produced in accord with the teachings ofU.S. Patent 2,351,290-Rippl et al. Likewise, the bulbs of the seconddescribed embodiment wherein the combustible material comprises onlybeads 7 may be produced in accord with the aforementioned patent 2,-29l,983-Pipkin.

While I have described the invention with reference to certainembodiments thereof many modifications will occur to those skilled inthe art. Accordingly, I intend by the appended claim to cover all suchmodifications as come within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A photoflash lamp comprising an hermetically sealed lighttransmitting envelope; an oxygenous atmosphere Within said envelope; anda charge of a combustible material within said envelope sufi'icient, oncombustion within said envelope, to produce actinic light of abrightness corresponding to that of a black body radiator at thecombustion temperature of thorium, said material comprising unoxidizedthorium metal having purity of at least 2. A photoflash lamp comprisingan hermetically sealed light transmitting envelope; an atmosphere ofoxygen within said envelope, and a charge of a combustible actinic lightproducing material within said envelope sufficient, on combustion withinsaid envelope, to produce actinic light of a brightness corresponding tothat of a black body radiator at the combustion temperature of thorium,said material comprising unoxidized thorium.

3. A photoflash lamp comprising an hermetically sealed lighttransmitting envelope; an atmosphere of oxygen within said envelope,anda charge of a combustible actinic light producing material withinsaid envelope sufficient, on combustion Within saidenvelope, to produceactinic light of a brightness corresponding to that of a black bodyradiator at the combustion temperature of thorium, said materialcomprising unoxidized thorium; said thorium and said oxygen beingpresent in proportions of 5 to 25 mg. of thorium per cubic centimeter ofoxygen at atmospheric pressure.

References Cited by the Examiner UNITED STATES PATENTS 594,594 11/97Bostwick 14919 613,021 10/98 Schwartz l499 1,77 6,637 9/ 30 Ostermeier673l 2,012,866 8/35 Decker 149-42 2,071,369 2/ 37 Williams et al 6731 72,272,779 2/42 Sarbey 6731 2,813,412 11/57 Johnson 6731 FOREIGN PATENTS14,972 10/06 Great Britain.

OTHER REFERENCES Metal Progress: Non-Nuclear Uses of Thorium, by W. C.Lilliendahl, February 1957, pp. 104-107, vol. 71, No. 2, pub. byAmerican Society for Metals, Mount Morris, Ill.

EDWARD J. MICHAEL, Primary Examiner. PERCY L. PATRICK, Examiner.

2. A PHOTOFLASH LAMP COMPRISING AN HERMETICALLY SEALED LIGHTTRANSMITTING ENVELOPE; AN ATMOSPHERE OF OXYGEN WITHIN SAID ENVELOPE, ANDA CHARGE OF A COMBUSTIBLE ACTINIC LIGHT PRODUCING MATERIAL WITHIN SAIDENVELOPE SUFFICIENT ON COMBUSTION WITHIN SAID ENVELOPE, TO PRODUCEACTINIC LIGHT OF A BRIGHTNESS CORRESPONDING TO THAT OF A BLACK BODYRADIATOR AT THE COMBUSTION TEMPERATURE OF THORIUM, SAID MATERIALCOMPRISING UNOXIDIZED THORIUM.